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Full text of "Alaskan glacier studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and lower Copper River regions"

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338
ALASKAN GLACIER STUDIES
retreat of Toboggan Glacier will be facilitated by the black slate ledge at the northern end of the medial moraine. A good point from which to measure, in case of advance of the glacier, is the nearest graywacke ledge to the north (e, Fig. 48) which was 517 feet from the ice front in 1910, and is a low roche moutonnee, beautifully striated. There are other graywacke ledges further west.
The low moraine described by Grant seems to have been destroyed by the glacial streams between 1909 and 1910.
In front of the southwestern portion of the Toboggan Glacier, an area of parallel furrows and minute ridges similar to those seen by Gilbert at Columbia Glacier, had been exposed by melting since 1905. They extended north and south, disappearing under the edge of the ice, and were made of till and outwash gravel containing fragments of finely-shredded wood. About 70 feet from the ice front, and parallel to it, was
farren-zone. /.ajf Moraine
FIG. 48.   MAP OF Lowma END OF TOBOGGAN GLA.OIEE IN 1010. Showing outwash delta, moraines and abandoned stream gorges.
a diminutive ridge, 6-12 inches high, crossing the erosion furrows nearly at right angles. It suggests either a crevasse deposit or a minute terminal moraine, probably the former.
Abandoned Marginal Gorges. In former times Toboggan Glacier was undoubtedly a tributary of the large ice tongue of Handman Fiord, and at a later stage, though disconnected, it was both longer and wider than now, as is shown by the barren zone about its borders. On the eastern side of the glacier, outside this barren zone, are two abandoned stream courses (c and d, Fig. 48), occupied by marginal drainage at a time when the glacier was more expanded than now, but later than the period when it extended up to the barren zone.
Barren Zone. A barren zone around both the eastern and western borders of Toboggan Glacier bears sparse vegetation which furnishes evidence of two stages in the history of the glacier. Outside the barren zone is mature, close-set forest, with thick moss but without undergrowth, the trees, which are from 11 to 19 inches in diameter, probably